69 vs 74

[louisb]

So I have all the stuff ready for the 1835 for the Manx buggy and now I am wondering if it might be worth it to swap out the 69mm CW crank for a 74mm CW crank. I figure I could do that without too much trouble at this point, just not sure it would be worth it.

The rest of the engine:

Stock rebuilt rods
92 thickwall AA P&Cs
Webcam 163 (between a 110 & 120)
40 idfs w/ 32 vents
010 dizzy
1.5 trimill bobtail exhaust (non-merged)
stock rockers
8.5 comp w/ .060 deck
Jeff Denham 40x35 heads, oval port nonwelded

The only reason I was thinking of adding it was for more bottom end and to take advantage of my UD heads.  I don't care about power over 6,000, I also don't want to change any other components or do extra machine work. The 74 w/ stock rods should only require minor clearance work and should go together pretty easy. I don't think I would have to run overly thick barrel spacers but width isn't an issue anyway. What do you guys think? Worth the extra $300?

Thanks,

--louis

[RFbuilt]

92x74 sounds very "porschey"   with that alone.. il say go for it!   

i think the extra 300$ expense, could be lesser, once all is said and done  you can sell ur 69cw crank too to recover sum $

simple math

100    mm (from crank centerline to deck/base of case hole)
112.5 mm barrel length
------------------------------
212.5  mm 
- 137   mm (rod length)
-  37    mm (stroke/2)
-  39.6 mm (piston pin height/compression height for A pistons)
= 1.1mm out of the barrel 
or

0.043" out of the hole,  would need just a 0.090" barrel spacer to put u in a groovy 0.046" deck/quench ? ur right, it wont be much of a issue the small width addition 

sounds good?  ofcourse this is a very very rough estimate, 212.5 isnt always accurate, sum end up at 212.2mm etc but its a good way of having an idea  short of actually mocking it up

ok ....i  ....must .... shut up 

[kingsburgphil]

Sounds pretty old school  Have you considered a 78x92b VW rod configuration? Cheap and easy to
build 

[louisb]

I thought about the 78 but I don't want to have to change the pistons and it would mean the case would have to be sent off for machining which I want to avoid.

--louis

[kingsburgphil]

Fair enough, I think anything better than a 40hp will still put a smile on your face. BTW thanks for letting the rest
of us share in your project 

[dyno don]

save yourself some money and call DPR in santa ana,ca 714-979-9441 and ask for Jose and tell him you want the "dyno don" special non c/w 74 crank...or have someone closer to you perform the service...you DONT NEED counterweights with your engine design and I would also change down your exhaust to 1 1/2 for better bottom end and driving experience with those heads. I would also recommend 8 dowel to the crank. I JUST did a recent engine with simular parts and it was a blast to drive. enjoy...

[louisb]

Thanks for the input Dyno, I will look into it.

--louis

[Zach Gomulka]

A Porsche journal 74 with shorter 136mm Porsche rods would work great, require little clearancing, and minimal shimming. Be very old school, too! Jose @ DPR also does a 73mm crank with chevy rod journals. With short 5.325's it would probably go together like a stocker.

I say keep it simple and stay with what you've got. Your buggy will be a blast with an 1835

[Diederick/DVK]

I say keep it simple and stay with what you've got. Your buggy will be a blast with an 1835

true, i thought monkiboy's manx back then with a single DCN 1641 was a blast. can you imagine a manx with an 1835 or 1968cc.
good luck though!

[louisb]

KISS

That is probably the answer I needed to hear.

--louis

[Kafur1]

I used a 74 scat crank and scat rods and did not hav to any grinding on the case